Perfusion-weighted magnetic resonance imaging is a common imaging technique used in the clinical treatment of patients with brain pathologies such as stroke or cancer. Perfusion-weighted images are obtained by injecting a bolus of gadolinium chelate into a patient's bloodstream and imaging as it passes through the brain. The gadolinium acts as contrast dye due to its T2 and T2* effects, which cause a drop in transverse relaxation time. This signal drop can then be used to calculate the concentration of the dye in a given voxel of brain tissue over time. The resulting concentration-time curves are then used with standard tracer kinetic models to calculate perfusion metrics such as blood volume, blood flow, and mean transit time.
However, solving the tracer kinetic model equations to calculate blood flow requires the deconvolution of an arterial input function from the measured concentration-time curves. Since the arterial input function is not known explicitly, it must be estimated from measured data. In current practice, a trained specialist examines the measured data and selects a single estimate of the arterial input function. This single estimate is used for the entire brain.
The current practice of estimating an arterial input function relies on the assumptions that the contrast agent reaches all parts of the brain at nearly the same time and that the contrast agent does not disperse significantly on its path from the major arteries to the brain tissue. In many cases, these assumptions are incorrect. However, even if the assumptions were correct, the time required to manually select the arterial input function can make the current practice inconvenient or impractical. In an emergency, the extra time spent identifying a suitable arterial input function could spell the difference between saving and losing brain tissue.